<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .demo a{
            float: left;
            display: block;
            height: 50px;
            width: 50px;
            border-radius: 10px;
            background: aquamarine;
            text-align: center;
            color: gray;
            text-decoration: none;
            margin-right: 5px;
            /*line-height:50px;*/
            font: bold 20px/50px Arial;
        }
        /*[属性名]，[属性名=属性值（正则）]
         = 表示绝对等于
         *= 表示包含
         ^= 表示以...开头
         $= 表示以...结尾
         存在id属性的元素
            a[]{}
            相当于a标签中带有那些属性的
         */
        /*a[id]{*/
        /*    background: yellow;*/
        /*}*/
        /*a[id=first]{!*id=first的元素*!*/
        /*    background: green;*/
        /*}*/

        /*a[class*=links]{!*class 中有links的元素*!
            background: bisque;
        }*/

        /*a[href^=http]{!*选中href中以http开头的元素*!
            background: bisque;
        }*/
        a[href$=pdf]{/*选中href中以http开头的元素*/
            background: bisque;
        }
    </style>
</head>
<body>
<p class="demo">
    <a href="http:www.baidu.com" class="links item first" id="first">1</a>
    <a href="" class="links item active" target="_blank " title="test">2</a>
    <a href="images/123.html" class="links item">3</a>
    <a href="images/1.png" class="links item">4</a>
    <a href="images/1.jpg" class="links item">5</a>
    <a href="abc" class="links item">6</a>
    <a href="/a.pdf" class="links item">7</a>
    <a href="/abc.pdf" class="links item">8</a>
    <a href="abc.doc" class="links item">9</a>
    <a href="abcd.doc" class="links item last">10</a>
</p>
</body>
</html>